Bug#595790: [Pkg-zfsonlinux-devel] Bug#595790: hostid: useless unless fixed

[Michael Stone <mstone@debian.org>]

On Wed, Sep 28, 2016 at 11:11:21PM +0200, Petter Reinholdtsen wrote:
> [Michael Stone]
> > Other platforms have deprecated gethostid, that's the best way forward for
> > linux, IMO.
>
> Which platforms is this?  I find FreeBSD recommend to use sysctl and
> KERN_HOSTID to get the hostid integer directly from the kernel instead
> of using gethostid(), which isn't really depricating the feature, only
> the way to get access to it.  A quick search did not show any other
> platforms depricating the function and feature, so I am curious to learn
> what those are.

openbsd deprecates it, netbsd doesn't have it at all. neither of those 
platforms is likely to have a useful value unless you set it yourself. 
I'd wonder where this *is* expected to be useful value more than I'd 
wonder where it isn't.

> My proposal is to use the DMI info which should stay the same
> independent of OS installation.

Which doesn't exist on many, many platforms. If you need an ID tied to 
the hardware that's the one to use, but you have to know that the 
hardware you're deploying to actually supports that feature.

> The users I am aware of is zfs-linux and the tools we wrote at work to
> detect when a Linux machine was reinstalled or had its hardware changed.

For the latter case, just use the smbios values directly (assuming 
you're buying enterprise style hardware, it should support machine 
uuids.) That way you know that you're getting something tied to the 
hardware, instead of hoping.

> The use case of zfs-linux require the ID to be unique among the machines
> sharing a storage solution, and not globally unique.

I can't understand why, for that use case, zfs-linux wouldn't simply 
create a uuid itself. I see no obvious advantage in the program trying 
to fix the semantics of a fundamentally broken function that was 
introduced in BSD in the 80s and was removed from BSD itself back in the 
90s.

> A search in the source of all Debian packages[1] show this list of 148
> packages mentioning the string 'gethostid': actiona alpine amanda
> apcupsd aplus-fsf arpwatch ats-lang-anairiats audit bacula bareos
> bluefish bsdgames burp busybox casacore cde cdrdao cdrkit
> chromium-browser cl-irc clisp cmucl condor coreutils ctwm cython dc3dd
> dcmtk deheader deja-dup dicom3tools dietlibc dist dmtcp dx e17
> eclipse-titan edk2 emscripten erlang facter fpc frama-c freebsd-utils
> freetds fs-uae ga gcc-h8300-hms gdb ghc glibc gnucash gnulib
> gnustep-netclasses golang golang-1.6 golang-1.7 golang-golang-x-sys
> hercules highlight hugs98 hurd iputils isdnutils ivtools kfreebsd-10
> krb5 ksh latrace ldc libcanberra libconvert-binary-c-perl
> libdata-uuid-perl libexplain libpam-tacplus libpcap libposix-2008-perl
> linux linux-grsec ltrace lua-posix manpages manpages-de manpages-es
> manpages-fr manpages-ja manpages-pl metview minc-tools mingw-w64 mono
> mono-reference-assemblies musl nam ncbi-tools6 netatalk newlib nim nmap
> nordugrid-arc ns2 ntirpc nwchem open-iscsi open-vm-tools openafs openmpi
> otp pidgin pidgin-nateon pimd polygraph praat prayer pulseaudio
> python-ptrace qemu radare2 rat roaraudio samhain sbcl silo-llnl sipxtapi
> slirp smlnj sniffit spl-linux splint strace talksoup.app tau tcpdump
> tcpslice tkrat topal trinity tripwire uclibc uclmmbase uhd uw-imap vde2
> xfsdump yap zephyr zfs-fuse zfsutils.
>
> I do not know what they use gethostid() for. :)

Pulling a couple at random:
libpcap -- the only occurance is in lbl/os-sunos4.h 
which is basically a list of function prototypes from a long obsolete OS 
for historic curiosity.

xfsdump -- honestly seems like a bug or at least a misunderstanding: 
ghdrp->gh_ipaddr = ( uint64_t )( unsigned long )gethostid( )

cdrdao -- questionable assumption in scsi-sun.c:
cpu_type = gethostid() >> 24

burp -- contains a couple of prototypes for the function, checks for it 
in configure, doesn't seem to actually use it

This really is a function with no current value that should just be 
forgotten. And certainly don't make random assumptions about the value 
it returns.

Mike Stone